1. Field of the Invention
The present invention pertains to the field of digital memory circuits. More particularly, this invention relates to providing an information storage unit having electrical marking for providing information, such as the content of the data stored in the information storage unit.
2. Background
Many consumer devices are now constructed to generate and/or utilize digital data in increasingly large quantities. Portable digital cameras for still and/or moving pictures, for example, generate large amounts of digital data representing images. Each digital image may require up to several megabytes (MB) of data storage, and such storage must be available in the camera. To provide for this type of data storage application, the storage memory should be relatively low in cost for sufficient capacities of around 10 MB to hundreds of gigabytes (GB). The storage memory should also be low in power consumption (e.g.  less than  less than 1 Watt) and have relatively rugged physical characteristics to cope with the portable battery powered operating environment. For archival storage, data need only be written to the memory once. Preferably the memory should have a short access time (in the order of milliseconds) and moderate transfer rate (e.g. 20 Mb/s). Preferably, also, the storage memory should be able to be packaged in an industry standard interface module, such as PCMCIA or Compact Flash card.
One form of write-once compact information storage is shown in U.S. Pat. No. 6,055,180, granted to Gudesen et al. on Apr. 25, 2000, in which matrices of individually addressable cells are provided in layers between orthogonally arranged conductors. The cells may be comprised of cross-point diodes, OLEDs, bistable liquid crystal elements or other devices that change state with the introduction of heat and/or light.
Another application in portable devices for providing high density archival storage is described in assignee""s U.S. Pat. No. 6,646,912 filed Jun. 5, 2001, entitled xe2x80x9cNon-Volatile Memory,xe2x80x9d the disclosure of which is hereby incorporated herein by reference. The memory system disclosed therein, referred to as portable inexpensive rugged memory (PIRM), aims to provide high capacity write-once memory at low cost for archival storage. This is realized in part by avoiding silicon substrates, minimizing process complexity and lowering areal density. The memory system includes a memory module formed of a laminated stack of integrated circuit layers constructed on plastic substrates. Each layer contains cross-point diode memory array, and sensing of the data stored in the array is carried out from a separate integrated circuit remotely from the memory module.
Because PIRM memory is relatively inexpensive, users will likely acquire a large number of PIRM modules with a variety of stored content. It is useful to browse the contents of the modules at a cursory level without having to insert the module into an appliance for a complete directory listing.
Accordingly, a display means is needed to indicate to the user the contents of the memory module. Typically it is important to have the display provide the nature of the data being stored in the memory module. The display may include the title, date of creation, location, type of data, owner and other descriptive information associated with the stored content. The display should also provide a display of the portion of the memory module that has been used, which can be depicted numerically, graphically or by other visual means. Preferably, the display information regarding the amount of memory used can be modified as the amount of stored data changes.
Prior solutions for labeling storage devices with content information all have their drawbacks. Hand-written adhesive backed labels are commonly used for recordable media, such as floppy discs, backup tapes and compact discs. This method is flexible and simple, but its resolution is limited by the user""s penmanship, and its accuracy is dependent on the user""s diligence in keeping it current.
Labeling photographic film may be accomplished by a small array of LEDs that print the date of the exposure directly on the negative. This approach detracts from the quality of the image and does not enable cursory browsing. Printing on the back of photo prints makes the information more accessible, but the print date is not likely to be the date the snapshot was taken. APS photographic film includes a magnetic tape stripe on the film for writing other forms of meta-data on the negatives. However, browsing is difficult without a scanner.
The tape cartridge for the linear tape open format provides a small amount of nonvolatile solidstate memory for diagnostic and crude directory information. This method avoids having to load and scan an entire tape, but it is still only readable with a machine.
CD rewritable and CD recordable have several content labeling methods, the simplest of which is a hand-written label on the disc. Alternatively, the plastic storage case can contain a printed sheet liner with content information. However, it is difficult to create this case liner and it can be easily separated from the case. CDs can also be labeled directly on the backing, but a complex process is required.
Prior art systems for indicating the used amount of a recording medium also have their limitations. CD-R devices provide a method for observing a subtle change in reflectivity of the disc in the area that has been recorded. However, this approach is so subtle that good lighting is required to determine the difference. APS photographic film provides an externally viewable annunciator that shows whether the film is unexposed, partially exposed, fully exposed or fully exposed and processed. Although this is useful information, the cost to implement the system involves complexity in the film cassette and requires the camera to detect the unexposed film.
Accordingly, there is a need for electronically labeling high density, portable and disposable memory modules to provide and display information about the content of the module and the extent to which the module memory has been used. Such labeling should be automatically carried out, readily visible and capable of displaying a variety of information. The display should also clearly indicate the amount of memory used and/or still available for use.
The present invention comprises an electrically addressable device for recording, addressing and reading of data, including a storage array unit having multiple layers of data storage medium, each of the layers being disposed on a substratet; and an electrical marking device on at least one of the layers of storage medium of the storage array unit to provide a display indicating pre-selected data or information, such as the nature of the content of the data stored on the storage array unit.
In one embodiment, the electrical marking device comprises at least one layer that is a display layer that is partially visually altered to provide a display of information, such as a display of the subject matter and name of the content of the data and the amount of memory storage that has been used.
The display layer comprises a plurality of information storage cells each representing the value of at least one data bit, wherein the visual appearance of the information storage cell varies depending on the state of the information cell. Each cell is a multiple state electrical device that changes states depending on the value of the data bit and has variable opacity, color and/or reflectivity, depending on the state of the electrical device. A suitable cell is comprised of an electrical fuse that has a modulated opacity depending on whether the fuse has been blown or that has a built-in marker to indicate that a fuse has blown. Preferably, the display layer comprises one of the outermost layers of the storage array unit. The storage array further preferably includes a reflective layer between the display layer and the next layer in the storage array unit.
In another embodiment of the present invention, each of the layers of the storage array device is disposed on a substantially transparent substrate, and the electrical marking device comprises an addressing device for storing the data on the storage array unit in a sequential manner across each layer of the storage array unit. The storage array device has corresponding data addresses at approximately the same location on each layer of the storage array unit and the addressing device simultaneously stores data on multiple layers of the storage array unit at approximately the same location on each layer. A reflective layer may be provided on at least one of the outermost layers of the storage array unit. The display indicates the amount of the memory module that has been recorded with data.
Another embodiment comprises a method for marking the content of an electrically addressable device used for recording, addressing and reading data and having a storage array unit with multiple layers of data storage medium. The method comprises storing data on an outermost layer representative of the content of the data to provide a display indicating the nature of the content of the data stored on the storage array unit. A reflective coating is preferably provided at the interface of the outermost layer and the remaining layers of the storage array unit. The display may indicate any pre-selected information, including but not limited to information about the subject matter and name of the content of the data, as well as the amount of the storage array unit that is recorded with data.
Other aspects and advantages of the present invention will become apparent from the following detailed description, which in conjunction with the accompanying drawings illustrates by way of example the principles of the present invention.